It all goes back to British money. In 1066, 945 years ago William the Conqueror divided our currency (the pound) into 20 shillings. The shilling was then divided into 12 pennies. Henry II changed it a bit a hundred years later, and based it on the troy system of weighing precious metals. A pound sterling thus weighed a pound of sterling silver, or 240 pennyweights. One penny weighed 1/240th of a pound of silver.



Nearly a thousand years later and it still causes confusion wordwide